Building on — 's answer:
Create a sprite, call it spawner.
Add the rotate behaviour to it and give it a value
Add the timer behaviour.
Add an instance variable "shoot" to the spawner and give a value for how often you want the spawner to shoot a bullet.
Create another sprite, call it bullet. Add the bullet behaviour to it.
Add the following code to your event sheet:
On (choose a trigger) set timer "shoot" to spawner.shoot (continuous)
On timer "shoot" : spawner| create bullet;
bullet|set bullet angle of motion to spawner; (make sure you use the bullet behaviour action here)
On (choose a trigger): stop timer "shoot".
You can then adjust the spawner rotate speed & direction and shoot variable, and the bullet speed to vary the pattern.
Use whatever triggers you want to start and stop the spawner.
For some variety try adding the sine behaviour to the spawner and use the angle, vertical or horizontal settings to move the spawner. Remember to remove/stop the rotate behaviour before doing this or things might go a bit weird - or maybe that's what you're after!